1. Field of the Invention
The present invention is directed to a liquid crystal display (hereinafter called "LCD") including thin film transistors (hereinafter called "TFT") as switching elements for applying a signal voltage to each pixel element in the display.
2. Description of the Related Art
An LCD comprising a plurality of pixel elements arranged in a matrix form, and a plurality of switching elements applying a signal voltage to each pixel element achieves a lightweight, low electric power consumption, high quality display image without flicker.
In these days, the LCD comprising pixel elements and driving circuits which are provided on the same substrate has been developed in order to ease the difficulty of connecting between the pixel elements and the driving circuits due to a decrease in the pixel elements' pitch.
A LCD having both fine pixel element pitch and high aperture ratio is described in "SID 90 DIGEST P.315-P.318; New Technologies for Compact TFT LCDs with High-Aperture Ratio".
Referring to FIGS. 5 and 6, the LCD of the prior art will be described. This LCD 901 comprises a pair of electrical substrates which are opposed to each other, and a liquid crystal composition 803 sealed in the gap between the pair of electrical substrates.
As shown in FIG. 6, a matrix array substrate comprises an insulating substrate, scanning lines 713a,713b and signal lines 711 being arranged in a matrix form on the insulating substrate, TFTs 721a,721b being connected to the scanning lines 713a,713b, respectively and the signal line 711, and pixel electrodes 751a,751b being connected to the TFTs 721a,721b, respectively.
In LCD 901, a pair of the scanning lines 713a,713b are closely disposed as one unit. Storage capacitor line 821 is disposed between adjacent pixel electrodes 751a,751b, the pixel electrode 751a being arranged on one side of the pair of the scanning lines 713a,713b and the pixel electrode 751b being arranged on the opposite side of the pair of the scanning lines 713a,713b.
According to the above conventional art, as mentioned above, the number of the storage capacitor lines 821 and contact holes 730 connecting between TFTs 721a,721b and signal lines 711 decreases to half of a conventional number.
In the above conventional art, as the LCD 901 is driven in a time-wise scanning fashion, i.e., the video signal is applied to the signal lines in sequence or in each block of the signal lines, the LCD 901 has to provide an additional signal storage capacitance (Cv) outside of the display area to hold the signal voltage for at least one scanning period. This is because the LCD 901 does not provide enough signal storage capacitance (Cv) in the display area to hold the signal voltage.
According to the above conventional art, a large electrode is need for the additional signal storage capacitance (Cv), and such additional storage capacitance (Cv) would result in a larger device size compared with the display area.
Upon decreasing the pixel electrode pitch, these constraints will become highly undesirable, because the LCD needs a prescribed capacitance for signal storage capacitance (Cv) independent of the pixel electrode pitch.
Moreover, in case of sealing a pair of the electrical substrates with sealing material being disposed between the display area and the driving circuits area surrounding the display area, the electrode for additional signal storage capacitance (Cv) would be broken by a glass fiber contained in the sealing material.